Surround view systems for passenger cars showing the vehicle from a bird's eye view are available from several manufacturers. A few solutions are also available for commercial vehicles, wherein multiple cameras are typically used to cover various sides of the vehicle. These multiple cameras may produce partially overlapping views that should be combined (synthesized) in the overlap areas to obtain a combined image. Otherwise, the two separate views of the same object may confuse the driver.
Although the creation of the bird's eye view of a vehicle is a common driver assistance application, in the area where the views of two cameras are to be combined together, the visibility of the objects is still not yet optimal. Due to the projection of the camera images to the ground, vertical objects are projected in the bird's eye view image in a way that they appear along a line extending away from the camera (i.e. radially from the camera ground point). Hence, at the location where the views of two cameras meet, the objects are projected into the areas, which are visible from the other camera. This may lead to a disappearance of the object in the bird's eye view.
Different methods are used by available systems for synthesizing the images into a single bird's eye view. A simple way is to separate the overlapping portions of the images with a straight line, and so to sidestep the problem, though at the cost of an abrupt change in the view as an object crosses the line. Another way is to allow an overlapping of the images, but to apply around the stitching line different kinds of blending procedures to obtain a transition from one camera view to the other.
Conventional blending procedures combine the images with a gradient transition from one image to the other by adding smoothly varying percentages of the different views in the overlapping area. This gradient blending area can be narrow (resulting in sharp transitions) or wide (resulting in slow transitions). For a narrow blending area a significant part of the object (e.g. an obstacle) may disappear, due to the projection of vertical images in the bird's eye view. On the other hand, in case of the wide blending, the obstacle may be seen twice (ghostlike).
Therefore, there is a demand for an image synthesizer, which overcomes the aforementioned problems and, in particular, generates a combined image that gives the driver confidences about the depicted scene.